Introduction to Fourier Transform Infrared ... - Nicolet CZ sro

Theory of FT-IRWhy Infrared Spectroscopy?Infrared spectroscopy has been a workhorse technique for materials analysis in the laboratoryfor over seventy years. An infrared spectrum represents a fingerprint of a sample withabsorption peaks which correspond to the frequencies of vibrations between the bonds of theatoms making up the material. Because each different material is a unique combination ofatoms, no two compounds produce the exact same infrared spectrum. Therefore, infraredspectroscopy can result in a positive identification (qualitative analysis) of every differentkind of material. In addition, the size of the peaks in the spectrum is a direct indication of theamount of material present. With modern software algorithms, infrared is an excellent toolfor quantitative analysis.Older TechnologyThe original infrared instruments were of the dispersive type. These instruments separatedthe individual frequencies of energy emitted from the infrared source. This was accomplishedby the use of a prism or grating. An infrared prism works exactly the same as a visible prismwhich separates visible light into its colors (frequencies). A grating is a more moderndispersive element which better separates the frequencies of infrared energy. The detectormeasures the amount of energy at each frequency which has passed through the sample.This results in a spectrum which is a plot of intensity vs. frequency.Fourier transform infrared spectroscopy is preferred over dispersive or filter methods ofinfrared spectral analysis for several reasons:• It is a non-destructive technique• It provides a precise measurement method which requires no external calibration• It can increase speed, collecting a scan every second• It can increase sensitivity – one second scans can be co-added together to ratioout random noise• It has greater optical throughput• It is mechanically simple with only one moving part3